Conventional photoimageable soldermasks, which may be applied in liquid form, typically contain 30-80% solids in solvents, such as naphtha, propylene glycol monomethyl ether, diglyme, and/or propylene glycol monomethyl ether acetate. These soldermasks require organic solvents to apply the mask to a substrate such as a circuit board or circuit board precursor and develop the masks. Some of the organic solvent evaporates and is lost to the environment. Of the total solvent lost to the environment, 85-95% of the solvent, is typically lost during the application process and 5-15% of the solvent is lost during the developing steps.
Recently, soldermasks have been devised that are designated "aqueous soldermasks". While they are developed using aqueous solvents, they are nevertheless applied using organic solvents. The use of such aqueous soldermasks reduces the solvent loss by only 5-15%. In contrast, a soldermask that is applied using an aqueous solvent, even though developed using an organic solvent, would reduce the overall organic solvent emissions by 85-95%.
It is desirable to have a soldermask that is applied using an aqueous solvent so as to reduce the emission of organic solvents during the application process.